1. Field of the Invention
The present invention relates to an improvement of an auto-zoom camera incorporating a function to automatically perform zooming by detecting defocus quantities in a plurality of areas within a picture and effecting a focal adjustment of a photographing lens.
2. Related Background Art
As an auto-focus detecting device of a camera, there has hitherto been well known a focus detection system for detecting a defocus quantity of an object. This involves imaging, on a couple of line sensors, beams of light coming from the object and passing through different exit pupil areas (focus detection areas) of a photographing lens and thereby obtaining a relative position shift quantity of a pair of image signals acquired by photoelectrically converting the object images. Known also is an auto focus adjusting method, wherein a plurality of these focus detecting systems are disposed, and the photographing lens is driven based on the defocus quantities detected with respect to a plurality of object positions.
Then, according to an element for selecting a focus detection area to be focused from the plurality of focus detection systems, there are a cases where the camera automatically selects at least one of a plurality of focus detection areas in accordance with a fixed algorithm and cases where a photographer takes a shot after designating the focus detection area beforehand.
There is also proposed a lens constructed such that the photographing lens serves as a zoom optical system, this is provided with a driving system, a zoom switch of the camera or the lens is manipulated, and the zoom can be thereby adjusted. In addition to manual operations by the photographer, this type of zoom lens is capable of a so-called auto-zoom, wherein the camera automatically adjusts a focal position.
This type of auto-focus camera presents, when selecting the focus detection area and performing the auto-zoom photography, the following drawbacks.
To be specific, when the photographer has some intention to take a picture and personally selects a focus detection area, if the zoom is automatically varied, the object undergoing the focus detection changes, with the result that an unintended action is induced. On the other hand, if an auto-zoom change switch is separately provided, zoom auto-/manual modes and focus detection area auto/manual modes have to be separately operated. This operation is quite troublesome.
Further, another problem arises. For instance, a focus detection area other than a central area is selected according to a focus detection area auto selection, and the focus is detected. In this case, when the zoom is varied, the object undergoing the focus detection changes, with the result that an unintended photo is taken. In the worst case, the auto focus detection area selection and the auto-zoom act on each other. Consequently, hunting occurs, or the object is out of a focus detection frame, resulting in a focus undetectable state in some cases.